High-angular resolution observations of Class 0/I protostellar jets with ALMA and NOEMA, like e.g. HH111, HH212, IRAS04166+ 2706, L1157 [1]}, [2]}, [3]}, [4]}, [5]}, [6]} bring strong evidence of time variability of the ejection process in the early protostellar phase.
A few observational estimates on timescales have been obtained, as illustrated by [6]}, who report an average value of \(310\pm 150\hbox{\hspace{1.99997pt}yr}\)  between subsequent ejection events in outflow C7 in the cluster Serpens South, with a large scatter in the knot distribution.
Also, in their study of a cluster of 46 outflow lobes in the star forming region W43-MM1 at \(5.5\hbox{\hspace{1.99997pt}kpc}\) , [8]} report clear events of episodic ejection. The typical timescale between 2 ejecta is estimated \(\approx 500^{+300}_{-100}\hbox{\hspace{1.99997pt}yr}\) , consistent with the values reported in nearby low-mass protostars. Uncertainties remain high because of the poorly constrained geometry and the outflow inclination angle with respect to the line of sight. Moreover, as noticed by the authors, outflows observed at increasing angular resolution turn out to present several spatial (thus temporal) characteristic scales. Therefore, more observational work is needed in order to make progress on these questions.
